Various types of motors have speed conrol systems coupled thereto in which the rotary speed of the motor is sensed by a transducer. The transducers provide signals representative of actual motor revolution, or motor speed, for comparison with command values in a closed control system. Such control systems provide signals which are representative not only of the deviation or error value, but also representative of the direction of operation of the motor. The operating direction of the motor can be represented by a signal which changes its sign, for example associates a 1-level value with one direction of rotation and a 0-level value with the opposite direction.
Speed transducers for use with rotary equipment may be opto-electrical or magnetic pulse transducers which, for each revolution of the motor, provide a predetermined number of pulses. The frequency of occurrence of the pulses is a measure of the speed. This signal, however, has no information regarding the direction of rotation, that is, the sign which the speed signal should have. Many drives are controlled in such a manner that the direction is also important, so that information regarding the sign is required.
Information regarding the direction of rotation may be obtained by providing two pulse transducers which are angularly offset with respect to each other, so that the phase relationship of the signals derived from the respective transducer can be analyzed and, then, the direction of rotation determined.